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    Alcohol determination via covalent enzyme immobilization on magnetic beads
    (Elsevier Science Sa, 2008) Kiralp, Senem; Topcu, Asuman; Bayramoglu, Guelay; Arica, M. Yakup; Toppare, Levent
    Alcohol oxidase was covalently immobilized onto magnetic beads of two different sizes, 75-150 mu m and 50-75 mu m in diameter, fabricated in the presence of glycidylmethacrylate and methylmethacrylate via suspension polymerization in the presence of a cross-linker (i.e., ethylenedimethylmethacrylate). The activity of the enzyme on smaller microspheres was found to be almost 4.8 fold higher than that of the larger counterparts. Although enzyme loading was same for both fractions, activity and the affinity of immobilized enzyme were significantly altered. The effects of various parameters such as temperature, pH, operational and storage stability were examined. The substantial change in the activity of enzyme was also observed in stability experiments in favor of large size magnetic beads. For all stability experiments including storage stability, the 75-150 mu m fraction was found to be more sentinel support for the enzyme. (C) 2007 Elsevier B.V. All rights reserved.
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    Covalent immobilization of chloroperoxidase onto magnetic beads: Catalytic properties and stability
    (Elsevier, 2008) Bayramoglu, Guelay; Kiralp, Senem; Yilmaz, Meltem; Toppare, Levent; Arica, M. Yakup
    Amino groups containing magnetic beads were used in covalent immobilization of the enzyme "chloroperoxidase (CPO)" which is one of a few enzymes that can catalyse the peroxide dependent oxidation of a wide spectrum of organic and inorganic compounds. The magnetic poly(glycidylmethacrylate-methylmethacrylate-etbyleneglycol dimethacrylate), magnetic p(GMA-MMA-EGDMA) beads were prepared via suspension polymerization in the presence of ferric ions. The magnetic beads were characterized with scanning electron microscope (SEM), Fourier transform infrared (FTIR), Mossbauer spectroscopy and vibrating sample magnetometer (VSM). The magnetic beads were derivatized sequentially with ammonia and glutaraldehyde, and CPO was covalently immobilized on the support via reaction of the amino groups of the enzyme under mild conditions. The effect of various parameters including pH, temperature and enzyme concentration on the immobilization efficiency of CPO onto glutaric dialdhyde activated magnetic beads was evaluated. Magnetic measurement revealed that the resultant CPO-immobilized magnetic beads were superparamagnetic with a saturation magnetization of 18.2 emu/g. The analysis of FTIR spectra confirmed the binding of CPO on the magnetic beads. The maximum amount of immobilized CPO on the magnetic beads was 2.94 mg/g support. The values of Michaelis constants Km for immobilized CPO was significantly larger, indicating decreased affinity by the enzyme for its substrate, whereas V-max values were smaller for the immobilized CPO. However, the CPO immobilized on the magnetic beads resulted in an increase in enzyme stability with time. (c) 2007 Elsevier B.V. All rights reserved.